Philadelphia is the largest city in the Commonwealth of Pennsylvania, the fifth-most-populous city in the United States, and the core of the sixth-largest metropolitan area in the country. Located in the Northeastern United States at the confluence of the Delaware and Schuylkill rivers, Philadelphia is the economic and cultural center of the Delaware Valley.
Philadelphia was one of the nation's capitals during the Revolutionary War, and the city served as the temporary U.S. capital while Washington, D.C., was under construction. During the 19th century, Philadelphia became a major industrial center and railroad hub that grew from an influx of European immigrants. It became a prime destination for African Americans during the Great Migration and surpassed two million occupants by 1950.